Quantitative and qualitative evaluation of nine different extraction methods for nucleic acids on soya bean food samples

Deoxyribonucleic acids (DNA) and ribonucleic acids (RNA) as normal compounds of many foodstuffs have so far been of minor interest with respect to human and animal nutrition. Through the approval of various genetically modified crops in the United States and Europe in recent years, these nucleic acids (NA) have become an important tool in food analysis. The reason for this is that in most cases the discrimination between a genetically modified foodstuff and an unmodified one can best be achieved directly at the:DNA level by means of proving the presence or absence of the introduced gene(s). So far, the various methods that can be used to purify DNA for such types of analysis have rarely been compared in a comprehensive manner. In this work the effects of nine different extraction methods on yield and quality of previously purified high-molecular-weight DNA from soya beans and of total NA from tofu, soya flour and lecithin have been tested. Quantification was accomplished using UV absorption at 260 nm and quality assessment of the DNA was done by polymerase chain reaction (PCR) with the soya bean-specific lectin 1 system. Using this approach we assessed the limits of DNA amplification for each food sample extracted using different extraction protocols. It was demonstrated that extraction methods using NA-binding resins like Wizard or DNeasy resulted in comparatively low yields. However, the DNA extracted with these methods is of high quality and suitable for downstream processing like PCR. Simpler and faster methods resulted in relatively high yields of NA but of relatively poor quality. Inhibition of PCR was observed due to one of the buffers used during NA extraction. Finally, the different extraction methods used in this study were compared with respect to the costs and the time needed to perform the extractions.